BACKGROUND OF THE INVENTION
[0001] The present invention relates to a continuous hot-dip plating apparatus and, more
particularly, to a continuous hot-dip plating apparatus having a roll assembly which
has superior resistance to erosion caused by a molten metal and also to wear caused
by friction between a roll shaft and bearings.
[0002] In general, a roll, which has portions being supported by a bearing, and bearings
are made of metals. This applies also to the case of a roll of a hot-dip plating (or
coating) apparatus or a hot dipping apparatus which is used in a plating molten metal.
Therefore, the shaft of a plating roll of a hot- dip plating apparatus, as well as
bearings in support of the shaft, are provided with a layer of a material having a
high resistance to erosion, e.g., a stainless steel, high-chromium steel and so forth,
formed by a pad welding or provided as a sleeve. Unfortunately, however, even such
an erosion resistant material exhibits erosion during long use as a result of contact
with the molten metal or the friction between the roll shaft and the bearings, with
the result that the clearance between the roll shaft and the bearings is undesirably
increased. Generally, the clearance between the roll shaft and the bearings grow to
an unacceptable level within four days when used continuously in a plating bath of
molten aluminum and within seven days when used in a plating bath of molten zinc.
In consequence, vibration is generated as a result of rotation of the roll shaft,
with the result that a uniform plating on steel strips is failed.
[0003] In order to avoid this inconvenience, it has been necessary to temporarily suspend
the plating operation to allow renewal of the roll shaft and the bearings. Such suspension
of operation undesirable impairs the production efficiency, increase in the production
of unacceptable products due to stop of the plating line, much money and labor for
the renewal of the roll shaft and the bearings, and so forth, with the result that
the production cost is undesirably raised.
[0004] In order to reduce erosion and wear, various proposals have been made in, for example,
Japanese Utility Model Unexamined Publication (called JITSUYO KOHKAI) Nos. 60-35917
and 60-196029, as well as in Japanese Patent Unexamined Publication (called TOKKYO
KOHKAI) Nos. 62-205254 and 62-205255. On the other hand, Japanese Patent Unexamined
Publication (called TOKKYO KOHKAI) Nos. 60-298626 and 61-92320 disclose the use of
a ceramics material as the material of the sliding surface layer of bearings in a
continuous hot-dip plating apparatus, to make an effective use of the multiplied
advantages of ceramics: namely, erosion resistance and wear resistance. Japanese Patent
Unexamined Publication (called TOKKYO KOHKAI) Nos. 60-298626 and 61-92320 also disclose
the use of ceramics as the surface materials of inner and outer races and roller elements
of a roller bearing which is intended for use under severe conditions such as high-temperature
and corrosive conditions. The roller bearings disclosed in these patent specifications,
however, employ impractically large number of parts and have to meet strict requirements
for dimensional precision of parts, resulting in a raised production cost. The coating
of rolling surfaces of the parts encounters with a problem in that the thickness of
the coating layer is undesirably limited. It is also to be noted that wear in amount
of several microns to ten or more microns can easily take place even in the case of
ceramics. Thus, a considerably frequent renewal is required also with the case where
the rolling parts are coated with ceramics. In addition, the above-mentioned two patent
specifications fail to disclose in what manner the rolling parts are coated with
ceramics, as well as the selection, dimensions and evaluation of ceramics. Thus, these
specification do not show any process for forming a roll bearings having a ceramics
layer.
SUMMARY OF THE INVENTION
[0005] In general, a roll shaft and supporting bearings of a continuous hot-dip plating
apparatus, which are used in the plating bath of a molten metal, suffer from erosion
caused by the molten metal, as well as heavy wear of the sliding surfaces due to load
applied to the sliding portions of the roll shaft and the bearings as a result of
application of a large tensile load to the steel strip which is to be plated. The
erosion and/or wear of the sliding part undesirably increases the clearance between
the roll shaft and the bearings, with the result that stable operation of the plating
apparatus is impaired due to vibration caused by the rotation of the roll shaft.
[0006] Accordingly, it is a principal object of the present invention to provide a continuous
hot-dip plating apparatus in which corrosion- and wear-resistances of the sliding
parts of the roll or the roll shaft and the bearings which are used in a plating bath
of a molten metal is improved to ensure a longer life of the roll and/or the bearings.
The extended life of the roll and/or the bearing reduces the frequency of the renewal
so that the yield or production efficiency is improved by virtue of the fact that
the frequency of renewal of the worn parts and, hence, the period of suspension of
the operation of the continuous hot-dip plating apparatus are reduced. In addition,
the rate of generation of the unacceptable products attributable to frequent stopping
of the plating line is reduced, whereby the cost incurred for the purpose of replacement
of the roll is reduced to lower the production cost.
[0007] According to the invention, the above-described objects are achieved by providing
a ceramic layer on the sliding portions of a metallic roll shaft which are held in
sliding contact with the bearings and/or on the surfaces of which slidingly support
the above-mentioned sliding portions of the roll shaft.
[0008] According to one aspect of the present invention, there is provided a continuous
hot-dip plating apparatus having bearings held in a bath of a melt of a plating metal,
and a roll rotatably supported in the bath by the bearings, wherein the improvement
comprises that a clearance exists between each the bearing and the roll shaft, the
clearance being of a size which enables the melt to come into the clearance during
rotation of the roll, and that a ceramics as a sliding member is provided on at least
a portion of the surface of the metallic bearing shell of the bearing.
[0009] According to the second aspect of the present invention, there is provided a continuous
hot-dip plating apparatus having bearings held in a bath of a melt of a plating metal,
and a metallic roll rotatably supported in the bath by the bearings, wherein the
improvement comprises that a clearance exists between each the bearing and the roll
shaft, the clearance being of a size which enables the melt to come into the clearance
during rotation of the roll, that a ceramics as a sliding member is provided on at
least a portion of the surface of the metallic bearing shell of the bearing, and that
a ceramics as a sliding material is provided on each of the sliding surfaces of the
roll supported by the bearing.
[0010] According to the third aspect of the present invention, there is provided a roll
bearing for use in sliding contact with another member within a bath of a melt of
a plating metal in a continuous hot-dip plating apparatus, wherein the bearing is
made of a ceramics and at least the sliding surface of the ceramics is left in as-sintered
state without being machined.
[0011] According to the fourth aspect of the present invention, there is provided a method
of using a roll bearing for use in sliding contact with another member within a bath
of a melt of a plating metal in a continuous hot-dip plating apparatus, wherein the
sliding portion of the bearing is composed of a ceramics in the form of a sleeve or
a plurality of rings, the ceramics being periodically moved in the rotational direction
so as to allow adjustment of the sliding contact between the bearing and a roll shaft
carried by the bearing, thereby preventing any uneven wear of the sliding portion
of the bearing.
[0012] According to the fifth aspect of the present invention, there is provided a roll
assembly for use in a continuous hot-dip plating apparatus, the assembly including
bearings held in a bath of a melt of a plating metal, and a roll rotatably supported
in the bath by the bearings, wherein at least one of each sliding surface of the roll
shaft and the sliding surface of the associated bearing is made of a ceramics having
a large wettability to the melt of the plating metal.
[0013] According to the sixth aspect of the present invention, there is provided a roll
assembly for use in a continuous hot-dip plating apparatus, the assembly including
bearings held in a bath of a melt of a plating metal, and a roll rotatably supported
in the bath by the bearings, wherein at least one of each sliding surface of the roll
shaft and the sliding surface of the associated bearing is made of a porous ceramics
having open pores formed thereon.
[0014] According to the seventh aspect of the present invention, there is provided a roll
assembly for use in a continuous hot-dip plating apparatus, the assembly including
bearings held in a bath of a melt of a plating metal, and a roll rotatably supported
in the bath by the bearings, wherein at least one of each sliding surface of the roll
shaft and the sliding surface of the associated bearing is made of a ceramics having
minute holes formed thereon.
[0015] According to the eighth aspect of the present invention, there is provided a roll
assembly for use in a continuous hot-dip plating apparatus, the assembly including
bearings held in a bath of a melt of a plating metal, and a roll rotatably supported
in the bath by the bearings, wherein at least one of each sliding surface of the roll
shaft and the sliding surface of the associated bearing is made of a ceramics having
fine grooves formed thereon.
[0016] The bearing shell is in general made of an iron containing metal or a steel material,
preferably from a stainless steel or a chromium steel which have high resistance to
erosion. The ceramics is mounted on a metallic bearing shell in the form of a sleeve.
A ring or a plurality of shell-like segments on a plurality of circumferential portions
suffers from the heaviest wear.
[0017] According to the invention, the roll may be made either from a metal or from ceramics.
Wear of the roll shaft, however, requires the plating line to be stopped so that the
roll shaft also is preferably made from a ceramics which is resistant to wear.
[0018] The ceramics for use as the material of the sliding parts in the continuous hot-dip
plating apparatus of the present invention should exhibit superior resistance to wear
in the molten metal bath, as well as resistance to wear at high temperatures. The
ceramics suitably used are: oxide type ceramics such as Al₂O₃, BeO, ZrO₂, MgO, CaO,
Cr₂O₃, 3Al₂O₃.2SiO₂, MgO.SiO₂ and 2Mg
0.2Al₂O
3.5SiO₂; carbide type ceramics such as SiC, B₄C, TiC, WC, VC and ZrC; nitride type ceramics
such as Si₃N₄, AlN, TiN and ZrN; boride type ceramics such as BN, ZrB₂ and TiB₂; and
later-mentioned composite ceramics represented by Sialon, Si₃N₄-BN, Sialon-BN, Sialon-SiC
and so forth.
[0019] Each of the ceramics mentioned above exhibits superior resistance to erosion in a
molten metal bath, as well as high resistance to wear when used under a condition
where lubrication by melt is available, as compared with iron containing metals. The
lubrication by melt and, hence, wear resistance equivalent to that obtained under
a lubricated condition, however, cannot be obtained with a random selection of these
ceramics. Namely, various factors such as the strength, wear resistance, easiness
of production, and purpose and conditions of use have to be considered in selecting
the ceramic material. In regard to the easiness of the production, high formability
and sinterability are essential for the purpose of producing large-size ceramic sleeves.
[0020] The first viewpoint of the present invention is related to a common understanding
that the rate of erosion of ceramics is closely related to the degree of wetting of
the ceramics with metal melt, more specifically, that the smaller the wettability,
the greater the erosion resistance. For instance, wettability of SiC, Al₂O₃, Si₃N₄
and BN becomes smaller, i.e., wet contact angle becomes greater, in the mentioned
order when these ceramics are used together with molten aluminum. From this point
of view, it is considered that the use of Si₃N₄ or BN is preferred when the continuous
hot-dip plating is conducted with molten aluminum. According to the first viewpoint
of the invention, it is preferred to use ceramics known as sialon, generally expressed
by Si
6-zAl
zO
zN
8-z (Z ≦ 4.2), which exhibits small wettability to Al and Zn which are broadly used
as plating metals.
[0021] The second viewpoint of the invention is related to the fact that the wear-resistance
of a sliding member is significantly ruled by the friction coefficient of the sliding
surfaces. Among various factors which affect the friction coefficient, the effect
of lubrication is an important factor which should not be neglected. In general, the
friction between sliding parts which are dipped in a metal melt is considered as being
a melt lubrication friction. However, if both parts have small levels of wettability
to the melt, friction between these parts is as large as that in a dry friction, thus
causing heavy wear of these parts or part. From the second viewpoint, therefore, it
is preferred that the ceramics used in the invention preferably has a certain level
of wettability to the metal melt, though such a wettability tends to impair the erosion
resistance to some extent. Needless to say, the wet contact angle between a metal
melt and a ceramics varies depending on conditions such as the kind of the metal melt,
plating condition and so forth. It is therefore advisable to select a suitable ceramics
which has a small angle of contact.
[0022] From a synthetic point of view including both the first and second viewpoints, it
is preferred that both sliding parts are made of ceramics which exhibit small wettability
to the metal melt and that these parts are constructed to invite the metal melt into
the gap between these parts and to hold the same in the gap, thereby realizing a melt-lubricated
sliding condition. Such a construction can be obtained by using a porous ceramics
material, or by forming a multiplicity of indentations, holes and/or grooves in the
surface of the ceramic material by a post-machining, so that the metal melt can be
held in the pores, indentations, holes and/or grooves.
[0023] Other objects, features and advantages of the present invention will become clear
from the following description of the preferred embodiments when the same is read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024]
Fig. 1 is an illustration of a continuous hot-dip plating process employing a continuous
hot-dip plating apparatus of the present invention;
Fig. 2 is a sectional view of an essential portion of a continuous hot-dip plating
apparatus of the present invention;
Fig. 3 is a diagrammatic illustration of a manner in which wear of a metallic sink
roll bearing and wear of a metallic sink roll shaft proceed in the continuous hot-dip
plating apparatus shown in Fig. 3;
Fig. 4 is a chart illustrating the results of a slide friction test conducted with
various materials;
Fig. 5 is a perspective view of a ceramic sleeve incorporated in an embodiment of
the present invention;
Fig. 6 is a sectional view showing an essential portion of the continuous hot-dip
plating apparatus, illustrating particularly the manner in which the ceramic sleeve
shown in Fig. 5 is mounted on a bearing shell;
Fig. 7 is an illustration of the relationship between the ceramic sleeve fixed on
the bearing shell and the roll in the state of use;
Fig. 8 is an illustration of another example of the manner in which the ceramic sleeve
is mounted on a bearing shell;
Fig. 9 is a sectional view taken along the line IX-IX of Fig. 8;
Fig. 10 is a perspective view of a bearing ceramics segment used in another embodiment
of the present invention;
Fig. 11 is a sectional view of an essential portion of the embodiment illustrating
the manner in which the ceramic segment of Fig. 10 is mounted on a bearing shell;
Fig. 12 is an illustration of a manner in which a plurality of ceramic segments are
mounted on a bearing shell;
Fig. 13 is a graph showing the results of a test showing the wettability of various
ceramic materials to molten Al;
Fig. 14 is a graph showing the results of a sliding friction wear test conducted with
various ceramic materials;
Fig. 15 is a sectional view of a roll shaft having a sleeve mounted on portions thereof
which make sliding contact with bearings; and
Fig. 16 is a sectional view of a bearing shell having ceramics segments on portions
thereof which slidingly support a roll.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Fig. 1 illustrates a continuous hot-dip plating process including a continuous hot-dip
plating apparatus 10. A steel strip 12 to be plated is continuously rinsed through
an inlet rinsing zone 1 which is composed of a rinsing tank, a scraper and an electrolytic
rinsing tank, and is taken-up by a pay-off reel 2 past a welder, a cutter and a leveler.
The strip 12 paid-off from a pay-off reel 2 is sent to the hot-dip plating apparatus
10 through an annealing furnace 3. the strip 12 which is hot-dip-plated through the
apparatus 10 is taken-up by a tension reel 9 through a surface adjusting device 4,
a bridge roll device 5, an SPM 6, a tension leveler 7 and a formation processing device
8. The plating apparatus 10 is shown in Fig. 2 in a greater scale. The strip 12 which
is fed through a snout 11 is turned around a sink roll 14 of a sink roll device in
a plating bath contained in a plating tank 13 and is taken out of the tank 13. A support
roll 15 of a support roll device serves to stabilize the running of the strip 12 which
is running out of the plating bath after turning around the sink roll 14. The strip
12 taken out of the plating bath is made to pass through a wiping nozzle 17 which
serves to regulate the plating thickness. Since the molten metal of the plating bath
serves as a lubricant for lubricating the sliding portions between the shaft 18 of
the support roll and the sink roll device and the associated roll bearing shells 19,
slide-type bearings are most commonly used as the roll bearing shells 19.
[0026] A careful examination of the conventional sink roll bearing has proved that the wear
of the roll bearing takes place and progresses in the direction of the vector of force
which is generated as a result of tuning of the strip 12 around the sink roll 14 (see
the arrow A in Fig. 2).
[0027] In Fig. 3, the states of progress of the wear of the wear of the sink roll bearing
shell 19 and the sink roll shaft 18 are illustrated by hatched areas.
[0028] Example of the invention worked out from the first viewpoint mentioned before, as
well as the results of a test conducted with such an embodiment, will be described
with specific reference to Examples 1 to 5.
EXAMPLE 1
[0029] The selection of the ceramics as the material of the sliding parts is one of the
most important factors. Sliding wear characteristics exhibited by various materials
in a molten metal bath were therefore examined through an experiment. The test was
conducted by pressing test pieces of various materials to a side surface of a disk
rotated in a metal melt. The test conditions were as follows.
Size of rotary disk: |
100 mm diameter and 5 mm thick |
Size of test pieces: |
30 mm long, 30 mm wide and 5 mm thick |
Contact pressure: |
50 kg/cm² |
Sliding speed: |
15 m/min |
Kind of metal melt: |
Aluminum |
Test temperature: |
700°C |
[0030] A bearing steel JIS SUJ-2 was used as the material of the rotary disk. On the other
hand, the task pieces were fabricated from the following materials: a material JIS
FC-25 as an example of ferrous material, materials JIS S 50C, JIS SUJ-2 and JIS SUS
304 as examples of steel materials, a material SiC as example of a carbide-type ceramics,
Al₂O₃ and ZrO₂ as examples of oxide-type ceramics, and materials Si₃N₄, sialon Si₃N₄-BN
and sialon-BN as examples of nitride-type ceramics and composite ceramics. Fig. 4
shows the results of the wear test. As will be seen from Fig. 4, the amount of wear
increases as the sliding distance increases but the rate of growth of the wear varies
according to the materials. Thus, the materials can be sorted into the following three
types from the viewpoint of the relationship between the sliding distance and the
depth of wear.
(i) Ferrous and steel materials
(ii) Ceramics materials of oxide and carbide types
(iii) Ceramics of nitride type and ceramics of composite nitride-based ceramics.
[0031] The metallic materials (i), which were conventionally used, were tested for the purpose
of comparison with the ceramic materials. It will be seen that any of the ceramic
materials tested showed superior wear resistance as compared with the conventionally
used metallic materials. It will also be seen that the nitride-type ceramic materials
and composite type ceramic materials showed greater wear resistance than those exhibited
by oxide- and carbide-type ceramics. The ceramic materials of nitride type and nitride-based
composite-type ceramic materials are, for example, ceramics such as silicon nitride
(Si₃N₄) and composite ceramic materials containing, as its major component, silicon
nitride, e.g., sialon, Si₃N₄-BN and sialon-BN which is a material composed of 90 wt%
of sialon and 10 wt% of BN.
EXAMPLE 2
[0032] A test was conducted by using a ceramic sleeve 20 (see Fig. 5) as a sliding member
used in the present invention. The test was executed by mounting this ceramic sleeve
20 on the sliding surface of a bearing shell 19 of the sink roll device of the type
shown in Fig. 2.
[0033] A ceramic material selected from the group of the nitride-type and composite-type
ceramic materials which showed superior effect as shown in Fig. 4, in particular,
sialon ceramics which showed superior formability and sinterability, was used as the
material of the ceramic sleeve 20. More specifically, the sialon ceramics is a material
which is expressed by Si
6-zAl
zO
zN
8-z, where Z can be varied within the range of 0 to 4.2 and which is generally referred
to as β-sialon.
[0034] To explain in more detail, in this Example, a powder of sialon of the above-mentioned
formula (Z = 0.5) was mixed with a small quantity of binder, and mixture was wet-kneaded
in a methanol, and then granulated by a spray drying method. The granules were then
compacted to a piece having an outside diameter of 250 mm, inside diameter of 170
mm and a length of 250 mm by means of a cold isostatic press. The thus formed piece
was then subjected to a provisionally baking and was then machined by a lath to a
predetermined size which was determined taking into account a dimensional change which
may be caused through the final baking, as well as finishing margin. The final baking
was conducted at 1750°C. Since the baking temperature approximates the thermal decomposition
temperature of silicon nitride, the formed material tends to be thermally decomposed
to become a metal silicon and blow holes are tend to be formed in the sintered body
as a result of the relief of the metal silicon. In order to avoid such a thermal decomposition,
the final baking was executed in an atmosphere composed mainly of nitrogen gas.
[0035] Fig. 5 shows the appearance of the sintered body 20 after finish machining. The finished
sintered body or the ceramic sleeve had an outside diameter of 200 mm, an inside diameter
of 150.6 mm and a length of 200 mm. The inner peripheral surface of the ceramic sleeve
thus formed was not subjected to any machining and was tested in as-sintered state.
Namely, the inner peripheral surface of the ceramic sleeve had circularity and cylindricity
of 0.3 mm or less in terms of errors, as well as a surface state of 7S or finer, thus
well meeting general requirements for bearing surfaces which are intended for use
in a molten metal bath. In this Example, the finish machining was conducted to such
that the ceramic sleeve becomes to have an outside diameter and a length which well
conform with those of the bearing shell 22. Such final machining, however, is not
essential and the ceramic sleeve of this Example may be used without any final processing.
The ceramic sleeve was then subjected to a machining for forming through- holes 21
from the outer to inner sides of the sleeve in eight rows which are equi-spaced in
the circumferential direction, each row including three holes. Thus, 24 through-holes
were formed in total. Each through-hole 21 was a non-threaded hole of 10 mm dia. and
the opening thereof in the inner peripheral surface of the sleeve 20 was machined
to a depth of 8 mm as measured from the sleeve inner surface at an angle of 45° to
receive an oval counter-sunk head of a bolt.
[0036] Fig. 6 illustrates a manner in which ceramic sleeve 20 is mounted on a bearing shell
22 by means of bolts 24 screwed into a corresponding threaded hole 23 in the shell
22. Namely, the ceramic sleeve 20 was fixed to the bearing shell 22 by means of counter-sunk
head bolts 24 each having an overall length of 30 mm, length of threaded portion of
20 mm, length of head of 6 mm and an outside diameter of threaded portion of 8 mm.
The mounting work was executed at a normal temperature and a clearance of 1 mm in
terms of radius was left between the wall of the through-hole and the bolt. A material
JIS SUS 304 was used as the material of the bearing shell so that the difference in
the thermal expansion coefficient between the ceramic sleeve and the bearing shell
was about 9 x 10⁻⁷/°C. Thus, no excessive stress is caused by fastening with bolts
when the temperature is raised to the level of the temperature for plating with aluminum
or zinc.
[0037] Fig. 7 schematically shows a roll shaft 18 of the invention for continuous hot-dip
plating in accordance with the present invention.
[0038] The ceramics sleeve was mounted on the bearing shell such that it extends in parallel
with the roll axis, by making use of four out of eight rows of through-holes, i.e.,
12 through-holes. The roll shaft 18 was processed such that a gap of 1 mm in terms
of radius is left between the inner sliding surface of the ceramic sleeve 22 and the
roll shaft 18. Thus, a clearance of 2 mm at the maximum exists between the roll shaft
18 and the roll bearing 20. In operation, the metal melt 16 of the plating bath is
allowed to come into this clearance so as to perform lubrication. The roll shaft used
in this test was made of a steel JIS SUJ-2.
[0039] A description will be given of the results of a test conducted to confirm the advantages
of the present invention. A sink roll device having a roll bearing of the present
invention was used in a continuous plating in molten aluminum of 680°C, together
with a conventional roll bearing made of a steel. While the conventional steel roll
bearing exhibited a wear of about 15 mm in four days, the roll bearing of this invention
showed a wear on the order of about 0.6 mm which is as small as 1/25 that of the conventional
roll bearing.
[0040] The roll bearing of the invention was used continuously for twelve days without replacement.
The depth of wear was 1 mm or less, thus proving superior effect of the present invention.
[0041] In order to confirm another advantage of the present invention, the ceramic sleeve
20 after 12-day use was taken out of the roll bearing and was used again after a circumferential
shift of the position in amount of 1/8 of the circumference. No abnormal wear was
found in this case, and the amount of wear after 12-day use in this new position was
not greater than 1 mm, as is the case of the wear at the initial position. It is thus
possible to use the same ceramic sleeve 20 for eight times while avoiding any increase
in the wear. If the inner surface of the ceramic sleeve is machined after repetition
of use for eight times to recover the circularity and cylindricity of the sleeve,
the sleeve can become usable again, thus allowing repeated use of ceramic sleeves
which is expensive.
[0042] Although the ceramic member was used in the form of a sleeve, this is only illustrative
and the ceramic member may be used in the form of a semi-circular or semi-cylindrical
member, without substantially impairing the advantages of the present invention.
In such a case, however, the ceramic member cannot be used repeatedly unlike the case
of the cylindrical ceramic member. It is also possible to compose the ceramic sleeve
from a plurality of coaxial ceramic rings.
EXAMPLE 3
[0043] In Example 2 described hereinbefore, the invention was applied to a sink roll device.
In Example 3, the invention is applied to a support roll device which is used in a
continuous hot-dip plating bath.
[0044] The material and the production process of the ceramics member are materially the
same as those of Examples 1 and 2. A test was conducted by using a ceramic sleeve
mounted on the support roll bearing and a segment-type ceramics member provided on
the support roll shaft. The ceramic sleeve had an outside diameter of 120 mm, an inside
diameter of 92 mm and a length of 100 mm. The ceramics member on the roll shaft in
the form of segments had an outside diameter of 90 mm, an inside diameter of 70 mm,
a length of 100 mm and a width of 25 mm. The test was executed in accordance with
a routine work in a hot-dip plating bath of aluminum of 680°C. After a 12-day use
of the test sample, the roll and the bearing were extracted for the purpose of measurement
of wear in the sliding parts of the ceramics. The wear was measured to be 0.3 mm or
less, thus proving the advantage of the present invention.
EXAMPLE 4
[0045] In Examples 2 and 3, the ceramic sleeve was fixed to the bearing shell by means of
bolts. A test, however, was conducted by fixing the ceramic sleeve by other means
that the bolts, as will be understood from the following description of Example 4.
I this Example, a ceramic sleeve 20 was used which had an outside diameter of 200
mm, an inside diameter of 150.6 mm and a length of 210 mm. A plurality of notches
or recesses 25, each having a depth of 10 mm and a width of 15 mm, were formed in
one axial end surface of the ceramic sleeve 20 at a constant circumferential pitch
or interval. As shown in Fig. 8, the bearing shell 22 had a central cavity for mounting
the ceramic sleeve 20 therein. The diameter of the cavity of the bearing shell was
200.5 mm. Thus, a clearance was left between the ceramic sleeve 20 and the bearing
shell 22 for easy mounting and demounting of the ceramic sleeve 20. Thus, the ceramic
sleeve 20 could be used repeatedly by being rotated through a predetermined angle
after use at each rotational position. Steel blocks 26 serving as retainer tabs, each
being 13 mm wide, 8 mm high and 25 mm long, were welded at 90° interval to the axial
end surface of the bearing shell 22 adjacent to the axial end of the ceramic sleeve
20 where the notches or recesses 25 were formed. The ceramic sleeve was then fitted
in the central cavity of the bearing sleeve from the opposite side to the blocks 26.
Since the blocks 26 are sized to loosely fit in the recesses 25, no excessive stress
was caused even at the operation temperature. As shown in Fig. 9, the axial end of
the ceramic sleeve 20 opposite to the recesses 25 was retained by a pair of blocks
26. This, however, is not exclusive and the sleeve may be retained by means of, for
example, a ring plate or the like member. The test was conducted under the same conditions
as Example 2, and the same results as Example 2 were confirmed, thus proving the advantages
of the invention regardless of the difference in the method of mounting the ceramic
sleeve.
EXAMPLE 5
[0046] A plurality of ceramic segments 20 of the type shown in Fig. 10 were mounted on a
bearing shell 22 in support of a sink roll device of Fig. 2, in a manner shown in
Fig. 12. Sialon was used as the ceramic material in this case.
[0047] The composition of the sialon is expressed by Si
6-zAl
zO
zN
8-z, where Z is variable within the range of 0 to 4.2, and is generally referred to as
β-sialon. More specifically, in this Example, a sialon powder of the above-mentioned
formula (Z = 0.5) was mixed with a small quantity of binder and the mixture was wet-kneaded
in methanol followed by granulating by spray-drying method. Subsequently, the granulated
material was pressed by a cold isostatic press so as to be formed into a piece of
25 mm long, 62 mm wide and 250 mm long. The piece was then baked at 1750°C for five
hours. This baking temperature is close to the decomposition temperature of silicon
nitride, so that the material tends to be thermally decomposed to become a metal silicon,
leaving blow holes after the relief of the silicon. In order to avoid this undesirable
effect, the baking was executed in an atmosphere mainly composed of a nitrogen gas.
[0048] Fig. 10 illustrates the appearance of the ceramic segment obtained after final machining.
The ceramic segment thus obtained had a length of 20 mm, width of 50 mm and a length
of 200 mm. Three through-holes 21 were formed in the sintered piece at an interval
of 50 mm in the longitudinal direction of the ceramic segment. Each through-hole 21
was an oval non-threaded hole having a longer axis of 10 mm and a shorter axis of
8.5 mm. One end of each through-hole was machined to a depth of 8 mm and at a taper
angle of 45° so as to form a recess capable of receiving the head of a counter-sunk
head bolt.
[0049] Fig. 11 illustrates a manner in which the ceramic segment 20 was secured to a bearing
shell 22. As shown, the ceramic segment 20 was fastened to the bearing shell 22 by
means of three bolts 24 which were driven into threaded bolt holes 23 formed in the
bearing shell 22. The bolt 24 was a counter-sunk head bolt 24 having an overall length
of 30 mm, length of threaded portion of 20 mm, length of head of 6 mm and a thread
outside diameter of 8 mm. The operation for fixing the ceramic segment 20 to the bearing
shell 22 was conducted at the room temperature. A clearance of 1 mm was left between
the wall of each non-threaded hole 21 in the ceramic segment and the bolt 24 as measured
in the direction of the longitudinal axis of the through-hole 21. An austenitic stainless
steel JIS SUS 304 was used as the material of the bearing shell. Thus, the difference
in the thermal expansion coefficient between the bearing shell and the ceramic segment
was 9 x 10⁻⁷/°C. When the interval or spacing of the bolts is 50 mm as in the illustrated
example, the thermal displacement caused when the segment is heated to plating temperature
suitable for plating with aluminum or zinc is about 30 µm at the greatest. It is therefore
possible to prevent generation of excessive stress through the ceramic segment as
fixed with bolts.
[0050] Fig. 12 shows a state in which the ceramic segments 20 were fixed to the bearing
shell 22. Namely, a piece of ceramic segment 20 was fixed to a portion of the bearing
shell 22 which is offset from the neutral or vertical axis of the bearing shell 22
by an angle of 18°, by means of bolts by making use of a recess and bolt holes which
have been beforehand formed in the bearing shell 22. In addition, a pair of pieces
of ceramic segment 20 were secured to both wing portions of the bearing shell at positions
about 20 mm apart from the lower ends of wings of the bearing shell 22. These three
pieces of ceramic segments 20 were arranged such that the inner surfaces of these
three segments define a circle of a diameter of 150 mm. The roll shaft was made of
a high carbon chromium bearing sheet JIS SUJ-2 and the diameter of the roll was 148
mm.
[0051] A test was conducted in order to confirm the effects of the present invention. A
continuous hot-dip plating was conducted by using a sink roll supported by bearings
of this Example, within a molten aluminum plating bath of 680°C. It was confirmed
that, while a conventional steel roll bearing showed a wear of a depth of about 15
mm after operation for four days, the roll bearing of this Example showed a wear of
about 1 mm which is as small as about 1/15 that of the conventional steel bearing.
The bearings of this Example were then subjected to a continuous 12-day operation
while the roll was changed at every four days. The depth of wear of the bearings after
the 12-day use was as small as about 1.5 mm, thus proving a remarkable improvement
in the life of the roll bearings.
[0052] Embodiments of the invention based on the aforementioned first and second viewpoints
of the invention will be described hereinafter through illustration of Examples 6
to 11.
EXAMPLE 6
[0053] The most critical factor of the invention is to select an appropriate ceramic material.
The inventors therefore measured, in an argon gas atmosphere, the "wet contact angle"
of various ceramic materials with each of a molten Zn plating bath of 700°C and a
molten Al plating bath of 1000°C. The ceramic materials tested were alumina (Al₂O₃),
zirconia (ZrO₂), beryllia (BeO), boron nitride (BN), silicon carbide (SiC), silicon
nitride (Si₃N₄) and sialon (Si
5.5Al
0.5O
0.5N
7.5). A test was also conducted in which test pieces of these ceramic materials were
dipped for 5 hours in each of the molten Zn plating bath of 700°C and the molten Al
plating bath of 1000°C and the depths of erosion of the test pieces were measured.
Each of the ceramic materials showed a wet contact angle approximating 180° with respect
to the molten Zn of 700°C. This means that the tested ceramic materials are materially
not wettable with molten Zn of 700°C. In addition, the depths of erosion of these
ceramic materials after the 5-hour dipping in the molten Zn of 700°C were generally
as small as 2 µm or less. The small wettability of these ceramic materials with respect
to molten Zn means that no substantial liquid lubrication effect can be expected when
these ceramic materials are used in a molten Zn plating bath.
[0054] Referring now to the molten Al bath of 1000°C, BN showed the greatest wet contact
angle (158°) among the tested ceramic materials, while the smallest wet contact angle
(34°) was exhibited by SiC. Thus, the wet contact angle largely varies depending on
the kind of the ceramics. In general, the ceramic materials which exhibit greater
wet contact angle showed smaller erosion depth. Likewise, the ceramic materials having
smaller wet contact angle showed greater erosion depth. Fig. 13 shows the relationships
between the erosion depth (abscissa) and the wet contact angle with respect to molten
Al (ordinate) as observed with the tested ceramic materials. It will be seen that
the erosion depth-wet contact angle characteristics of these ceramic materials are
plotted almost on or around a single curvilinear line. From Fig. 13, it will be seen
that BN, Si₃N₄ and Si
5.5Al
0.5O
0.5N
7.5 exhibit wet contact angles considerably greater than 90°, as well as small erosion
depths, thus proving small wettability of these ceramic material to molten Al. On
the other hand, oxide-type ceramic materials, i.e., Al₂O₃, ZrO₂ and BeO, and carbide-type
ceramic material, i.e., SiC, showed wet contact angle smaller than 90°, as well as
large erosion depths, thus proving that these ceramic materials have large wettability
to molten Al. From the first and second viewpoint of the invention mentioned before,
it is therefore understood that the object of the present invention can be achieved
by using an oxide-type or a carbide-type ceramic materials.
[0055] The wettability of the ceramic material also is affected by factors such as the surface
roughness, impurity content and density of the ceramic materials, as well as by the
described factors such as the kind and temperature of the molten metal.
EXAMPLE 7
[0056] An experiment was conducted to examine sliding friction wear resistance characteristics
of ceramic materials in a molten metal. The test was carried out by pressing test
pieces of various ceramic materials onto a side surface of a disk rotated at high
speed in a molten Al. The test conditions were as follows:
Size of rotary disk: |
diameter 100 mm, thickness 5 mm |
Size of test piece: |
30 mm long, 30 mm wide and 5 mm thick |
Contact pressure: |
10 kg/cm² |
Sliding speed: |
100 m/min |
Test time: |
5 hours |
Test temperature: |
1,000°C |
[0057] As the material of the rotary disk, Si₃N₄ which has a large contact angle was used.
The ceramics materials tested were Si₃N₄, Sialon, Al₂O₃, BeO, reaction bonded Si₃N₄(RBSN)
and a reaction bonded SiC(RBSC). The results of the test are shown in Fig. 14. From
this Figure, it will be seen that a heavy wear takes place when both of the materials
kept in sliding frictional contact have small wettability as is the case of the Si₃N₄
and Sialon, despite the use of the ceramic materials. Ceramic materials exhibiting
wet contact angles smaller than 90°, e.g., Al₂O₃, can be liquid-lubricated by the
molten metal so that the wear is reduced. A further reduction in the wear is attainable
with BeO and SiC. Namely, BeO and SiC exhibit wear which is smaller than half that
exhibited by Al₂O₃. In particular, the RBSN and RBSC having open pores can be impregnated
with molten Al so that they can be well lubricated with molten Al when used in the
molten Al bath, thus showing a remarkable reduction in the wear.
EXAMPLE 8
[0058] A ceramic sleeve 27 prepared in accordance with the present invention was fitted
to each sliding portion of a sink roll shaft 18, as shown in Fig. 15. On the other
hand, ceramic segments 20A prepared in accordance with the invention were fitted in
the sliding surface of bearing shells 22, as shown in Fig. 16. The sink roll shaft
18 with the ceramic sleeve 27 and the bearing shell 22 with the ceramic segments 20A
were assembled together and were tested for the purpose of confirmation of the advantages
of the present invention. The sink roll 14 used in this test had a barrel diameter
of 422 mm, barrel length of 1160 mm, journal diameter of 130 mm and a journal length
of 180 mm. An Ni-Cr-Mo steel tempered to exhibit a Brinell hardness of 320 was used
as the material of the sink roll 14.
[0059] Sialon was used as the material of the ceramic sleeve 27 of Fig. 15. The sialon is
expressed by Si
6-zAl
zO
zN
8-z, where Z is variable within the range of 0 to 4.2. This type of Sialon is generally
known as β-sialon. More specifically, in this Example, powder of Sialon expressed
by the above-mentioned formula, where Z being selected to be 0.5, was mixed with a
small amount of binder, and the mixture was wet-kneaded in a methanol. The kneaded
mixture was then granulated by a spray drying method. The granulated material as then
formed by a cold isostatic press at a pressure of 1,500 kg/cm². Thus formed material
was then provisionally baked and machined by a lath to a predetermined size taking
into account a dimensional change which will take place during the final baking, as
well as a finish machining margin. The final baking was conducted at 1750°C in a nitrogen
gas atmosphere. The ceramic sleeve thus finished had an outside diameter of 150 mm,
an inside diameter of 130.6 mm and a length of 180 mm.
[0060] The ceramic sleeve 27 was then mounted on the roll shaft 18 by a loose fit. The dimensional
relationship was carefully selected such that the ceramic sleeve 27 can make a tight
fit on the roll shaft without any risk of cracking when the roll shaft and the sleeve
are heated to 650°C, since the test was executed by operating the roll continuously
in a molten Al plating bath of 650°C.
[0061] On the other hand, the bearing as shown in Fig. 16 was prepared in the following
manner. BeO was used as the material of the ceramic segment 20A. Three pieces of the
ceramic segments 20A, each being 180 mm long, 50 mm wide and 20 mm thick, were mounted
on the bearing shell 22 as shown in Fig. 16. More specifically, one piece of the
ceramic segments 20A was fitted in a recess formed in a portion of the inner surface
of the bearing shell which is in the direction of the vector of the force produced
by the strip 12 which turns around the sink roll 14. After the mounting of these pieces
of ceramics segments 20A, the sliding surface of the bearing shell was ground by a
diamond abrasive tool of a grading of 5000 or so, such that the sliding surface of
the bearing has a radius of curvature which is about 0.5 mm greater than that of the
ceramic sleeve on the roll shaft.
[0062] The combination of the sink roll shaft and the bearing thus prepared was tested by
being subjected to a continuous plating operation in an Al plating bath of 650°C,
together with a combination of a conventional roll shaft and a conventional bearing.
While the conventional arrangement could stand only a very short use of four days,
the combination of the roll shaft and bearings prepared in accordance with the invention
could stand continuous 1-month operation without suffering from any abnormal wear,
thus enabling the plating layer to be formed uniformly and continuously.
EXAMPLE 9
[0063] In Example 9, RBSN was used in place of BeO which was used in Example 8. The RBSN
was prepared by adding a small amount of a binder to an Si powder of a mean particle
size of 0.8 µm, wet-kneading the mixture in a methanol, and granulating the kneaded
mixture by a spray drying method. The material as then formed into a piece by a cold
isostatic press at a pressure of 1,500 kg/cm² and thus formed piece was temporarily
baked in a nitrogen gas atmosphere and machined to a predetermined size. Since RBSN
does not exhibit any substantial dimensional change during the final baking, the machining
was executed to obtain a near-net shape which is almost the same in shape and size
as the final product except the provision of finishing margin. The final baking was
executed at 1380°C in a nitrogen gas atmosphere. Thus formed sintered member was then
shaped by grinding into the form of the ceramic segment of 180 mm long, 50 mm wide
and 20 mm thick, having an arcuate sliding surface. Thus formed ceramics segment had
pores of 50 to 100 µm at a porosity of about 17%. Thus formed porous segment was then
dipped in a molten Al bath of 650°C and a reduced pressure of 10 Torr was applied
thereto, so that the segment was impregnated with Al. The porosity is a factor which
significantly affects the lubrication performance. In order to attain an appreciable
lubrication effect, the porosity is preferably 5% or greater. On the other hand, a
too large porosity causes a reduction in the mechanical strength. The present inventors
have confirmed through an experiment that the porosity should not exceed 30% when
the porous sinter ceramics segment is used on the roll bearing of the type to which
the invention pertains. The porosity of the test pieces of the ceramic segment therefore
was adjusted to be not smaller than 5% but not greater than 30%. Thus prepared ceramic
segments were mounted on the bearing shell in the same manner as that in Example 8.
[0064] The combination of the sink roll shaft and bearings obtained through the described
process was subjected to a continuous plating in an Al plating bath of 650°C, together
with a combination of a conventional sink roll shaft and bearings. While the combination
of the conventional sink roll shaft and bearings become unusable after 4-day continuous
operation due to wear of the roll shaft and the bearings, the combination of the sink
roll shaft and the bearing prepared in accordance with the method of the present invention
could withstand 2- month continuous operation without suffering from any extraordinary
wear, thus enabling the plating to be conducted uniformly and continuously.
EXAMPLE 10
[0065] In Example 10, Sialon was used in place of RBSN having open holes used in Example
9. More specifically, in Example 10, minute holes having a hole size of 150 µm and
a depth of 1000 µm were formed at a spacing of 500 µm in the sliding surface, by means
of a laser machining. The sliding surface was then ground by a diamond abrasive wheel
of a grading of 5000 or so in amount of 10 µm in terms of diameter. Then, the segment
was dipped in an molten Al both of 650°C and a reduced pressure of about 10 Torr was
applied thereto so as to impregnate the segment with molten Al. Experiment was conducted
to seek for optimum values of the hole size, hole depth and the spacing of minute
holes, as well as the ratio of the area occupied by the minute holes, since these
factors significantly affect wear resistance and mechanical strength. It was confirmed
through the experiment that impregnation with Al cannot be effected satisfactorily
when the hole size is 20 µm or smaller and that a hole size exceeding 500 µm is not
preferred because such a large hole size tends to allow breakage of the segment under
the testing condition. It was also confirmed that minute holes of a too small hole
size cannot well retain the molten metal. Namely, it was found that the hole depth
should be equal to half the hole diameter, i.e., the hole radius, at the smallest.
It was found also that a too small spacing or pitch of the minute holes tend to cause
a breakage of the ceramics segment because of interference of stresses generated in
around adjacent minute holes. It was confirmed that the pitch of the minute holes
should be at least 2.5 times as great as the hole diameter. As to the ratio of the
area occupied by the minute holes, it was confirmed that the same requirement as that
for the open minute holes applies also to this case.
[0066] Pieces of ceramic segment thus prepared were mounted on the bearing in the same manner
as that in Example 9.
[0067] The sink roll shaft and bearings of this Example was used in an Al plating bath of
650°C for continuous plating operation. The combination of the sink roll shaft and
bearings of this Example could be used for a period which was more than 15 times longer
than that Exhibited by the conventional roll shaft and bearing.
EXAMPLE 11
[0068] In Example 11, fine grooves of a very small width were formed in the ceramic segment,
in place of the fine pores used in Example 10, and electrically conductive composite-type
ceramics, obtained by mixing 40% of titanium nitride in Sialon, was used as the material
of the ceramic segment. Using a discharge electrode, minute groove were formed spirally
in the sliding surface of the ceramic segment at a width of 150 µm, depth of 800 µm
and a pitch, i.e., distance between centers of adjacent grooves, of 500 µm. The sliding
surface was then ground in amount of about 10 µm in terms of diameter, with a diamond
abrasive tool of grading of 5000 or so.
[0069] Pieces of the segment were then impregnated with Al and mounted on the bearing shell
in the same manner as Example 10. This Example was subjected to a test conducted under
the same condition as Example 10, for the purpose of evaluation of the effect of the
fine grooves, and an effect equivalent to that produced by the pores in the preceding
Examples was confirmed. It was also confirmed that the longest life of the bearing
is obtained when the grooves are formed with a width of 20 to 500 µm, depth which
is at least half the width, pitch of at least 2.5 times as great as the width, and
a ratio of area occupied by the grooves of 5 to 30%.
[0070] It is also to be noted that the pores in Example 10 can be formed by an electric
spark machining, without impairing the effect. Similarly, an effect equivalent to
that produced by Example 11 can be obtained when the fine grooves are formed by a
laser machining rather than by the electric spark machining.
[0071] In Examples described hereinbefore, the ceramic members as sliding members can be
used in various forms such as a sleeve, a plurality of pieces of segments, and a plurality
of rings formed by slicing a sleeve. It is also possible to use a plurality of pieces
of segments which are arranged in the axial direction of the roll, although in the
illustrated Examples the pieces of segments are spaced in the circumferential direction.
[0072] Furthermore, an advantageous effect of lubrication in a molten metal bath can be
also achieved by impregnating a ceramics member with solid lubricants such as carbon
or molybdenum disulfide. Especially carbon is effective and preferable, since it can
be co-fired with ceramics.
[0073] As has been described, according to the present invention, a structure or a roll
assembly for use in a molten metal bath is proposed in which ceramics are used as
the material of the sliding portions of a metallic roll shaft and/or the sliding surfaces
of a metallic bearing in support of the roll shaft.
[0074] The ceramics used as the material of these sliding parts of the roll shaft and/or
the bearings improve the erosion and wear resistance of these sliding parts, thus
improving the durability of the roll shaft and/or bearings, so that the total cost
of production of plated steel strips is lowered advantageously. The advantage offered
by the present invention is remarkable particularly when a ceramic material having
a comparatively large wettability to the molten metal is used as the material of
the sliding portions of the roll shaft and/or the bearing.
1. A continuous hot-dip plating apparatus (10) having bearings held in a bath (16)
of a melt of a plating metal, and a roll rotatably supported in said bath by said
bearings, wherein the improvement comprises that a clearance exists between each said
bearing and roll shaft (18), the clearance being of a size which enables said melt
(16) to come into said clearance during rotation of said roll shaft, and that a ceramics
(20, 20A) as a sliding member is provided on at least a portion of the surface of
the metallic bearing shell (22) of said bearing.
2. A continuous hot-dip plating apparatus according to Claim 1, wherein said ceramics
is a ceramic sleeve (20) and is mounted on the bearing shell (22) of each of said
bearings coaxially with said roll so as to support ends of said roll.
3. A continuous hot-dip plating apparatus according to Claim 2, wherein said ceramic
sleeve (20) has a wall provided with a plurality of bolt-receiving through-holes (21)
arranged at predetermined intervals both in the axial and circumferential directions,
and is fixed to said bearing shell (22) by means of a plurality of bolts (24) driven
through said through-holes.
4. A continuous hot-dip plating apparatus according to Claim 3,wherein said through-holes
are sized and shaped such that predetermined clearance is formed between the wall
of each through-hole and the associated bolt, so as to prevent generation of excessive
thermal stress attributable to a difference in the thermal expansion coefficient between
the material of said bearing shell and the material of said sleeve.
5. A continuous hot-dip plating apparatus according to Claim 2, wherein said ceramic
sleeve (20) is provided in at least one end surface thereof with a plurality of recesses
(25) capable of engaging with retaining tabs (26) provided on said bearing shell (22),
whereby said ceramic sleeve is retained on said bearing shell through mutual engagement
between said recesses and said retaining tabs.
6. A continuous hot-dip plating apparatus according to Claim 5, wherein said recesses
and said retaining tabs are sized and shaped such that said retaining tabs are loosely
received in the associated recess so as to prevent generation of excessive stresses
in the axial and/or circumferential direction due to difference in the thermal expansion
coefficient between the material of said bearing shell and the material of said ceramic
sleeve.
7. A continuous hot-dip plating apparatus according to Claim 1, wherein said ceramics
is made of silicon nitride or a composite ceramics composed mainly of silicon nitride.
8. A continuous hot-dip plating apparatus comprising a sink roll device and at least
one support roll device placed in a bath (16) of melt of a plating metal, wherein
a sink roll (44) of the sink roll device is supported by bearings as set forth in
any one of Claims 1 to 7.
9. A continuous hot-dip plating apparatus comprising a sink roll device and at least
one support roll device placed in a bath of melt of a plating metal, wherein at least
one support roll (15) of the support roll device is supported by bearings as set forth
in any one of Claims 1 to 7.
10. A continuous hot-dip plating apparatus according to Claim 1, wherein said ceramics
includes a plurality of shell-shaped segments (20 in Figs. 10-12; 20A in Fig. 16)
which are arranged at least in the circumferential direction and mounted on said metallic
bearing shell.
11. A continuous hot-dip plating apparatus according to Claim 10, wherein said apparatus
comprises a sink roll device and at least one support roll device in a bath or melt
of a plating metal, and wherein one of said segments is located on the line of vector
of the force which is exerted on a sink roll of the sink roll device by a steel strip
(12) which is the product to be plated and which makes a turn around said sink roll.
12. A continuous hot-dip plating apparatus according to Claim 11, wherein each of
said segments (20 in Fig. 10) has at least one bolt-receiving through-hole 21) and
is fixed to said bearing shell by means of a bolt (24 in Fig. 11) driven through said
bolt hole.
13. A continuous hot-dip plating apparatus according to Claim 12, wherein said through-hole
formed in said segment is shaped and sized such that a predetermined clearance is
left between the wall of said through-hole and said bolt so as to prevent generation
of excessive stress in the axial and/or circumferential direction due to a difference
in the thermal expansion coefficient between the material of said bearing shell and
the material of said ceramic sleeve.
14. A continuous hot-dip plating apparatus having bearings held in a bath (16) of
a melt of a plating metal, and a metallic roll shaft (18) rotatably supported in
said bath by said bearings, wherein the improvement comprises that a clearance exists
between each said bearing and said roll shaft, the clearance being of a size which
enables said melt to come into said clearance during rotation of said roll, that a
ceramics (20, 20A) as a sliding member is provided on at least a portion of the surface
of the metallic bearing shell of said bearing, and that a ceramics (27) as a sliding
material is provided on each of the sliding surfaces of said roll shaft supported
by said bearing.
15. A roll bearing for use in sliding contact with another member within a bath (16)
of a melt of a plating metal in a continuous hot-dip plating apparatus, wherein said
bearing (20) is made of a ceramics and at least the sliding surface of said ceramic
is left in as-sintered state without being machined.
16. A method of using a roll bearing for use in sliding contact with another member
within a bath of a melt of a plating metal in a continuous hot-dip plating apparatus,
wherein the sliding portion of said bearing is composed of a ceramic in the form of
a sleeve or a plurality of rings, said ceramics being periodically moved in the rotational
direction so as to allow adjustment of the sliding contact between said bearing and
a roll carried by said bearing, thereby preventing any uneven wear of said sliding
portion of said bearing.
17. A roll assembly for use in a continuous hot-dip plating apparatus (10), said
assembly including bearings held in a bath (16) of a melt of a plating metal, and
a roll rotatably supported in said bath by said bearings, wherein at least one of
each sliding surface of roll shaft (18) and the sliding surface of the associated
bearing is made of a ceramic (27) material having a large wettability to said melt
of said plating metal.
18. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 17, wherein the wet contact angle of said ceramics to said melt of said plating
metal is not greater than 90°.
19. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 17, wherein said ceramics is made of ceramic material of oxide type or carbide
type.
20. A roll assembly for use in a continuous hot- dip plating apparatus (10), said
assembly including bearings held in a bath (16) of a melt of a plating metal, and
a roll rotatably supported in said bath by said bearings, wherein at least one of
each sliding surface of roll shaft (18) and the sliding surface of the associated
bearing is made of a porous ceramics having open pores formed thereon.
21. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 20, wherein said ceramics material has a porosity ranging between 5 and 30%.
22. A roll assembly for use in a continuous hot-dip plating apparatus (10), said
assembly including bearings held in a bath (16) of a melt of a plating metal, and
a roll rotatably supported in said bath by said bearings, wherein at least one of
each sliding surface of roll shaft (18) and the sliding surface of the associated
bearing is made of a ceramics having fine holes formed thereon.
23. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 22, wherein said fine hole has a diameter of 20 to 500 µm, a depth which is
greater than half of the diameter, spacing between the centers of adjacent holes of
at least 2.5 times as great as the diameter, and the ratio of the area of the surface
occupied by said holes of 5 to 30%.
24. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 22, wherein said fine holes are formed by processing by means of a laser beam.
25. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 22, wherein said fine holes are formed by processing by means of a discharge
electrode.
26. A roll assembly for use in a continuous hot-dip plating apparatus (10), said
assembly including bearings held in a bath (16) of a melt of a plating metal, and
a roll rotatably supported in said bath by said bearings, wherein at least one of
each sliding surface of roll shaft (18) and the sliding surface of the associated
bearing is made of a ceramics having fine grooves formed thereon.
27. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 26, wherein said fine groove has a width of 20 to 500 µm, a depth which is greater
than half of the width, spacing between the centers of adjacent grooves of at least
2.5 times as great as the diameter, and the ratio of the area of the surface occupied
by said holes of 5 to 30%.
28. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 26, wherein said fine grooves are formed by processing by means of a laser beam.
29. A roll assembly for use in a continuous hot-dip plating apparatus according to
Claim 26, wherein said fine grooves are formed by processing by means of a discharge
electrode.
30. A roll assembly for use in a continuous hot-dip plating apparatus according to
any one of Claims 22 to 29, wherein said ceramics has been ground after formation
of said holes or grooves.
31. A roll assembly for use in a continuous hot-dip plating apparatus according to
any one of Claims 20 to 30, wherein said ceramics is impregnated with said melt of
said plating metal which is charged in said open pores, said fine holes or said fine
grooves in advance of the use of said roll assembly.
32. A roll assembly for use in a continuous hot-dip plating apparatus according to
any one of Claim 31, wherein the impregnation is conducted in an atmosphere of a reduced
pressure.
33. A continuous hot-dip plating apparatus comprising a sink roll and at least one
support roll placed in a bath of melt of a plating metal, wherein said sink roll is
constructed together with said bearings as the sink roll device as set forth in any
one of Claims 17 to 32.
34. A continuous hot-dip plating apparatus comprising a sink roll and at least one
support roll placed in a bath of melt of a plating metal, wherein at least one of
said support rolls is constructed together with said bearings as the support roll
device as set forth in any one of Claims 17 to 32.